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Added more documentation regarding a REALLY annoying feature of JavaScript's string replace() method

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Jeff Parsons 2017-06-23 10:03:27 -07:00 • committed by Jeff Parsons
commit 5a22c9c59b
1 changed files with 20 additions and 7 deletions
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27
modules/pcx86/lib/keyboard.js
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@ -411,15 +411,23 @@ class Keyboard extends Component {
* *
* If you want any of those sequences to be typed as-is, then you must specify two "$" (ie, "$$"). * If you want any of those sequences to be typed as-is, then you must specify two "$" (ie, "$$").
* *
* WARNING: the JavaScript replace() function ALWAYS interprets "$" specially in replacement strings, even when * WARNING: the JavaScript replace() function ALWAYS interprets "$" specially in replacement strings,
* the search string is NOT a RegExp, and since we build machine definitions on a page from a potentially * even when the search string is NOT a RegExp; specifically:
* indeterminate number of string replace() operations, multiple dollar signs could eventually get reduced to a
* single dollar sign BEFORE we get here.
* *
* To compensate, I've attempted add 'replace(/\$/g, "$$$$")' operations where currently needed; eg, in the * $$ Inserts a "$"
* $& Inserts the matched substring
* $` Inserts the portion of the string that precedes the matched substring
* $' Inserts the portion of the string that follows the matched substring
* $n Where n is a positive integer less than 100, inserts the nth parenthesized sub-match string,
* provided the first argument was a RegExp object
*
* Since we build machine definitions on a page from a potentially indeterminate number of string replace()
* operations, multiple dollar signs could eventually get reduced to a single dollar sign BEFORE we get here.
*
* To compensate, I've attempted add replace(/\$/g, "$$$$") operations where currently needed; eg, in the
* markout.js convertMDMachineLinks() function, the htmlout.js addFilesToHTML() function, and the embed.js * markout.js convertMDMachineLinks() function, the htmlout.js addFilesToHTML() function, and the embed.js
* parseXML() function. Unfortunately, this is something that will be extremely difficult to prevent from breaking * parseXML() function. Unfortunately, this is something that will be extremely difficult to prevent from
* down the road. So, heads up to future me.... * breaking down the road. So, heads up to future me....
* *
* @this {Keyboard} * @this {Keyboard}
* @param {string|undefined} sKeys * @param {string|undefined} sKeys
@ -444,6 +452,11 @@ class Keyboard extends Component {
} }
sKeys = sKeys.replace('$' + match[1], sReplace); sKeys = sKeys.replace('$' + match[1], sReplace);
} }
/*
* Any lingering "$$" sequences are now converted to "$"; as discussed above, replace() interprets any
* "$$" in the replacement string as "$", so to the casual observer, it might not look like we're downsizing
* the dollar signs, but we actually are.
*/
sKeys = sKeys.replace(/\$\$/g, "$$"); sKeys = sKeys.replace(/\$\$/g, "$$");
} }
return sKeys; return sKeys;